Police in Russia are continuing to search for a missing candidate in next month's presidential election. The candidate, Ivan Rybkin, a strong critic of President Vladimir Putin, has not been heard from since last Thursday.

Family and friends of Ivan Rybkin say they lost all contact with him last week when he left his apartment in Moscow.

Mr. Rybkin is a 57-year-old former speaker of the lower house of parliament who was officially registered on Saturday as one of seven candidates in the March 14 presidential election. He is backed by controversial billionaire Boris Berezovsky, who now lives in England, where he was granted political asylum.

Mr. Berezovsky is one of the so-called oligarchs who amassed enormous fortunes under former President Boris Yeltsin a decade ago. He is a bitter opponent of President Putin.

According to public opinion polls, Mr. Rybkin has the support of only about one percent of Russian voters. He has been on the sidelines of Russian politics since losing his post as parliament speaker in 1996.

Last week, he launched his campaign for the presidency with a full-page open letter published in newspapers, saying that Mr. Putin is Russia's biggest oligarch and that he rules the country through fear.

Although Mr. Rybkin's wife, campaign manager and work colleagues say they have no idea where he is, a parliamentary colleague says he has heard Mr. Rybkin is spending time at a sanatorium, a kind of rest house, outside Moscow.

But no one has been able to confirm this report.

Mr. Rybkin was one of the last candidates registered by Russia's electoral commission over the weekend.

Others who received approval include the only liberal in the race, Irina Khakamada, who decided to run to protest what she calls Mr. Putin's authoritarian rule. Her party was all but wiped out in last December's parliamentary election, a vote that was criticized by international observers as not meeting democratic standards.

Others in the race are political unknowns from several parties whose main leaders decided to sit out the election, including the Communist Party.

Mr. Putin is expected to win a landslide victory. Seventy percent of Russians tell pollsters they approve of how he is running the country.